John McWhorter writes at The New Republic.com:

Of course, the question we are not supposed to ask is whether the failure rate suggests that black people are less intelligent. However, there is no need to fear here. The reason black people of unaffluent origin tend not to do well on standardized tests is a matter of language and how it's used—and the issue is less about color than class, and in the global sense, about what it is to be human.

In countless American communities, flyers are routinely full of major misspellings, more than a few people are only fitfully comfortable with e-mail, and few read newspapers above the tabloid level. Life is fundamentally oral. People from places like this (which include Appalachia and the rural white South, as much as black and brown inner cities) get next to no reinforcement from home life in acquiring comfort with the written word beyond the utilitarian.

Reading is not the only cultural hurdle. In working-class and poor black culture as in many fundamentally oral ones, being asked point-blank questions—like, "When was the Declaration of Independence written?"—and answering clearly is not as central to normal communication as it is in mainstream culture. (Consult, for example, Shirley Brice Heath's Ways With Words.) Many black people of working-class or poor background mention how ticklish this kind of interaction felt when they first went to a decent school.

Direct questions as regular interaction are largely an epiphenomenon of the printed page. Most humans on earth lead fundamentally oral lives in the linguistic sense (only about 200 of the world's 6,000 languages are written in any serious way, for example), and need to adjust to direct questions. Middle class American kids inhale them at the kitchen table. Other kids learn how to deal with them in school; it takes practice, and because our public schools are so uneven, quite a few never get really good at it.

Thus if the black firefighters aren't at home with the format of the promotion test (reading passages and answering questions on what they mean), it is understandable and has nothing to do with their innate ability. After all, placing 16th in a pool of several dozen candidates is not too shabby in itself. The job, it would seem—say, to old-time Civil Rights leaders with a black pride that deserved the name—would be to enhance the innate ability. The black candidates need practice.

Plaintiff Frank Ricci understood this. He's dyslexic. Instead of doing poorly on the test and charging discrimination, he had textbooks read onto tape, worked with a study group, and practiced hard. He placed sixth out of 77. Any notion that this is too much to ask of someone with more melanin—or even with a different "racial history"—is nonsensical at best and gruesome at worst.

Still, we justify the rhetorical contortions that excuse black people from challenging examinations; in the end, it is based on a tacit sense that such things are antithetical to black authenticity, that it is somehow untoward to require this kind of concentrated scholarly exertion on black people.

Okay, that may (or may not) be "the reason black people of unaffluent origin tend not to do well on standardized tests," but what about black people of affluent origin? Why is the racial achievement gap similar for them?

I've heard it argued a million times that racial differences in achievement are caused by socioeconomic differences, but when we look at blacks of high socioeconomic status, we see only fair-to-middling achievement.

For example, black college graduates who take professional and grad school exams only score at an average level of the 10th to 18th percentile among whites (depending upon the exam).

Thousands of social scientists have tried to make the racial gap disappear by adjusting for socioeconomic differences and have and failed. A social scientist who found a group of affluent African-Americans who consistently scored as well as whites of similar affluence would be feted for the rest of his life. The incentive is there, but nobody has been able to deliver the goods in 45 years of searching.

If you are black and you grew up summering in one of the small upper class black communities on Martha's Vineyard, then, yes, you'll do pretty well on average. You might do better on average than whites who never heard the word "summer" used as a verb. But, Martha's Vineyard blacks don't do as well on the whole on tests or in the real world as Martha's Vineyard whites. And it works that way up and down the social ladder.

Which then suggests, using Occam's Razor, that the socioeconomic gap is more caused by the achievement gap than vice-versa. But Occam's Butterknife remains much more popular...

One interesting question that McWhorter alludes to is whether African Americans are relatively more skilled at learning from oral than from written instruction. I could well believe that African Americans are better, relative to IQ, than whites at persuasive speaking, but I can't recall any evidence that they're better, relatively, at learning from listening than learning from reading. Perhaps, though, there is. I'm sure the topic has been studied at length.

In general, African American culture seems more oriented toward learning how to persuade other people subjectively than toward learning objective knowledge.